Most language learning studies indicates that strong language skills can be acquired only during a limited age range extending from early childhood to puberty (the critical period hypothesis). This research is concerned with the exceptions to this hypothesis, those adults whose ability to master languages in the absence of exposure during the critical period shows little or no diminishment after the critical age (proficient late bilinguals). The hypothesis to be tested in this study is that proficient late bilinguals utilize an additional neural pathway, common within their cohort but absent in most people. This research seeks to ascertain the existence of the specific neural pathways through which language learning is facilitated in proficient late bilinguals by mapping activations in fluent late bilinguals, as contrasted with weaker late bilinguals, by means of functional magnetic resonance imaging (fMRI) at 4.1 Tesla. The improved contract and resolution available with this high-field magnet will make it possible to detect smaller shifts in activation patterns with a higher degree of confidence. The differences in activation patterns between strong and weak bilinguals when performing various tasks in both languages will enable us to map patterns of cortical activation in each group by computing the differences in pixel activation as a function of the measured second language proficiency of the subject. This investigation will be limited to people introduced to a second language for the first time at an age past the critical period. To date, fluent and weak late bilinguals have not been compared directly in an fMRI study. It is expected to provide insight into the process by which hearing/speaking skills develop, which in turn may be applicable to understanding the causes and forms of some developmental language disabilities. The overall, long term objectives are twofold: first, to demonstrate that there is a neural substrate accounting for this difference in adult language learning ability' and second, to identify regions of the brain involved in language learning for each type of learner.